Universal joints, and especially constant velocity joints, operate to transmit torque between two rotational members. The rotational members are typically interconnected by a cage, or yoke, that allows the rotational members to operate with their respective axes at a relative angle. Constant velocity joints and similar rotating couplings typically include a boot cover assembly to enclose and protect the coupling during operation. The boot cover assembly is partially flexible and therefore able to seal around the joint while permitting articulation and relative axial movement of the joint. The boot cover assembly seals lubricant in the joint so as to reduce friction and extend the life of the joint. The boot cover assembly also seals out dirt, water and other contaminants to protect the functionality of the joint. However, leaks in the boot cover assembly may reduce the life of the joint, and contaminants in the grease may disturb the chemical composition of the grease, degrading its performance.
Indeed, a significant portion of constant velocity joint failures are due to damage to the boot. The boot is usually ruptured or cracked by impact with debris from the outside, such as stones or sticks. Alternatively, the boot sometimes cracks due to fatigue caused by the high stresses that are placed on the boot material when the joint is operated at high angles. If the boot cracks or ruptures, the lubricant located inside the joint will leak out, and cause corrosion or failure of the joint.